Python學習筆記（4）：控制流程

Python的控制語句有if、while、for、break、continue。

1. if語句

下面是一個猜數字遊戲例子：

# Filename: if.pynumber = 10guess = int(input("Enter a integer:"))if guess == number:    print("Congratulations, you guessed it.")elif guess < number:    print("No, it is a little higher than that")else:    print("No, it is a little lower than that")

注意if語句結尾處包含一個冒號（：），所有控制語句結尾處都需要冒號。Python沒有switch語句，您可以用if...elif...else來完成相同功能。

2. while語句

您可能發現上面猜數字遊戲，每次都要啟動一下才能猜，下面可以用while語句來控制直到你猜中才離開遊戲。

# Filename: while.pynumber = 10running = Truewhile running:    guess = int(input("Enter a integer:"))    if guess == number:        print("Congratulations, you guessed it.")        running = False    elif guess < number:        print("No, it is a little higher than that")    else:        print("No, it is a little lower than that")else:    print("The game is over.")

其實與while相對的else是多餘的，與直接把它的語句放在在while語句塊後面的效果相同。

3. for語句

# Filename: for.pyfor i in range(1, 5):    print(i)else:    print("The for loop is over.")

輸出結果為：

1

2

3

4

The for loop is over.

4. break語句

# Filename: break.pywhile True:    s = input("Enter something:")    if s == "quit":        break    print("Length of the string is", len(s))print("Done")

5. continue語句

# Filename: continue.pywhile True:    s = input("Enter something:")    if s == "quit":        break    if len(s) < 3:        continue    print("Input is of sufficient length")